moving clips on timeline causing crashes

I have a 90 minute 1920 x 1080/30P timeline. the source clips are 4k Xavc-I from for the most part an A7R II, an FS7 and GoPro 4+, with a bunch of stills mixed in. Everything has been going great through the edit, cutting 21 segments by themselves. I put all 21 segments on one time line for a master and when I try to select them all and move them down the timeline 30 seconds to make room for an AE open I'm crashing the program.

I tried "sneaking them down 10 seconds or so at a time and got away with it a couple times, but finally was "caught" by the spinning ball of UhOh! Any suggestions on how to do this without the tiny moves or?

XAVCi is simply the absolute worst codec to deal with in Premiere that there is right now. It simply had not yet gone through the process of getting optimized by the development team yet, and until it does, transcoding to ProRes 422 for HD, or HQ for 4K, is really the very best solution for now.

FYI, the Abobe development team are very much aware of the issue, but just have not yet gotten around to it yet. If you send a note to their bug fix address maybe you'll be the one who moves XAVCi to the top of their fix-it list.